The present invention relates to a method of forming a buried wiring and an apparatus for processing a substratum.
Studies are being vigorously made for decreasing a dielectric constant of an insulating interlayer used in a semiconductor device.
As one of the methods for decreasing the dielectric constant, studies are being made on the application of a porous insulating layer to an insulating interlayer. Having a low relative dielectric constant (∈), a porous insulating layer is expected to be promising as a raw material for decreasing a capacitance between wiring lines. In principle, a porous insulating layer is conventionally formed by a process of forming a porous structure having solid linkages on the basis of a solidification reaction according to dehydration/condensation in an aqueous solution containing tetraethoxysilane (TEOS) and ammonia (NH3), and then drying off the aqueous solution.
And, a metal wiring is formed by a so-called damascene process in which a lithography method and a dry etching method are used to form a groove (trench) portion and/or a hole portion in the porous insulating layer formed according to the above process, a barrier metal and a metal material such as aluminum and copper are filled in the groove portion and/or the hole portion and deposited on the porous insulating layer, and further, the metal material and the barrier metal deposited on the porous insulating layer are removed by a chemical/mechanical polishing method (CMP method).
Further, a hollow wiring method is available as one of the methods of decreasing the capacitance between wiring lines. In the hollow wiring method, an insulating interlayer between wiring lines is removed to bring the space between the wiring lines into a hollow state, and air which substantially has a relative dielectric constant of 1 is used as an insulating substance. This method is disclosed, for example, in xe2x80x9cSemiconductor Internationalxe2x80x9d, July 1999, page 125. This hollow wiring method is already put to practical use for broad aluminum wiring lines in which a wiring line width is several microns or more.
For overcoming problems in the hollow wiring method, there is proposed a method in which a hollow portion between wiring lines is filled with a solid insulating layer. In this method, metal wiring lines are formed in an insulating layer composed of a phosphorus silicate glass (PSG), and then, the insulating layer is removed by a drying etching method in which the insulating layer is exposed to a gas containing hydrogen fluoride (HF) or plasma thereof. At this stage, the space between the wiring lines is brought into a hollow state, and the space between the wiring lines is filled with a gas. Then, a porous insulating layer having a low relative dielectric constant is grown from the surface of the metal wiring line by a chemical vapor deposition method (CVD method) to fill the porous insulating layer in the space between the wiring lines.
In the method using an insulating interlayer composed of a porous insulating layer, however, it is difficult to form a groove portion and/or a hole portion having a desired form in the porous insulating layer under good control by a dry etching method. There is another problem that the porous insulating layer is damaged when a photoresist used in a lithography method is removed, so that the porous insulating layer is altered in chemical properties and form. For avoiding this problem, it is required to keep the porous insulating layer not being exposed to an atmosphere employed for the photoresist removal. For this purpose, an addition step is required. There is still another problem that, when a metal material and a barrier metal deposited on the porous insulating layer is removed by a CMP method, the porous insulating layer having low mechanical strength is broken due to a shear force exerted on the porous insulating layer. For preventing this problem, it is required, on a CMP process, to set a polishing rate at a level at which the shear force on the porous insulating layer is lower than a shear force which breaks the porous insulating layer. However, this procedure involves a problem that the polishing rate of the metal material and the barrier metal deposited on the porous insulating layer is decreased, which results in a longer throughput.
Further, the hollow wiring method has the following problem when it is applied to an LSI wiring having a wiring line width of 1 xcexcm or less. That is, a solution containing hydrofluoric acid is often used for removing a silicon-containing insulating interlayer, and a stress is caused between wiring lines due to a surface tension of water droplets formed between the wiring lines just before drying is finished in a drying step after a washing step. As a result, the wiring line may be mechanically deformed due to the above stress, which results in destruction. Further, if the drying is made possible by taking measures against the surface tension, the following problem takes place. That is, as the circuit operates, voltages of the wiring lines undergo changing. In this case, a local condenser having a potential difference between the adjacent wiring lines repeats charging and discharging, and due to the accumulation of a charge and the discharging, a Coulomb force between the adjacent wiring lines changes. As a result, the wiring lines vibrate, and when the vibration takes place intensely, the wiring lines may break due to the mechanical wearing of the wiring lines or a short circuit may be generated between the adjacent wiring lines. These problems make it difficult to apply the hollow wiring method to fine wiring lines in which a distance between the wiring lines is small.
In the method in which a hollow portion between wiring lines is filled with a solid insulating layer, a source gas used in the CVD method is fed from the top surface of each wiring line to side surfaces of each wiring line, so that an insulating layer is formed on the top surface earlier than it is formed on the side surfaces. Therefore, the insulating layer is formed on the top portions of the adjacent wiring lines before the insulating layer is formed in the bottom portions of the wiring lines and before a space between the lower portions of the adjacent wiring lines is filled with the insulating layer, so that a space between the upper portions of the adjacent wiring lines is filled with the insulating layer. As a result, there is caused a problem that there is a region which is not filled with the insulating layer between the wiring lines. Due to this problem, it is difficult to realize the technology of filling a hollow portion by removing the insulating layer in a gaseous phase and forming a new insulating layer in a gaseous phase. Further, there is another problem that a device isolation region and a gate insulating layer of a transistor portion are damaged with an etching gas used for removing the insulating layer by a dry etching method.
It is therefore an object of the present invention to provide a method of forming a buried wiring, in which high reliability is accomplished, the wiring is neither damaged nor broken, an insulating layer used for burying the wiring is not damaged, and an insulating material can be reliably filled between the wirings.
It is another object of the present invention to provide an apparatus for processing a substratum which apparatus is suitable for practicing the above method of forming a buried wiring.
According to the present invention, the above object of the present invention is achieved by a method of forming a buried wiring, which method comprises the steps of:
(A) forming a wiring and a first insulating layer filled between the wirings on a substratum,
(B) immersing the first insulating layer in a fluid which can dissolve the first insulating layer, to dissolve the first insulating layer into the fluid,
(C) substituting, for the fluid, a raw material solution containing a raw material for forming a second insulating layer, without bringing the wiring into contact with a gas, and
(D) filling a second insulating layer formed by gelation in the raw material solution at least between the wirings, and then, drying off the raw material solution, thereby to form the second insulating layer at least between the wirings.
The wording xe2x80x9cto form the second insulating layer at least between the wiringsxe2x80x9d includes the formation of the second insulating layer on the wiring. The wording xe2x80x9cdrying off the raw material solutionxe2x80x9d means the removal of a liquid component (for example, solvent) contained in the raw material solution.
In the method of forming a buried wiring in the present invention (to be sometimes referred to as xe2x80x9cforming method of the present inventionxe2x80x9d hereinafter), there may be employed a constitution in which the first insulating layer is composed of a silicon oxide material and the fluid (first-insulating-layer dissolving fluid) is an aqueous solution containing fluorine.
The silicon oxide material constituting the first insulating layer includes SiO2, BPSG, PSG, BSG, AsSG, PbSG, SbSG, NSG, SOG and SiON. The aqueous solution containing fluorine includes a 0.5 wt % hydrofluoric acid aqueous solution and a hydrofluoric acid buffer solution (mixture of HF and NH4F).
In the forming method of the present invention, there may be employed a constitution in which the first insulating layer is composed of an organic insulating material and the fluid (first-insulating-layer dissolving fluid) is one member selected from the group consisting of an amine-containing alkaline solution, a nitric acid aqueous solution and a mixture solution of hydrofluoric acid and nitric acid (a hydrofluoric acid/nitric acid/water volume ratio, for example, of 1:1:4), or the fluid (first-insulating-layer dissolving fluid) is one supercritical fluid selected from the group consisting of water, carbon dioxide, methyl alcohol, ethyl alcohol and oxygen.
The term xe2x80x9csupercritical fluidxe2x80x9d refers to a fluid having a temperature and a pressure a little higher than a critical point in a temperature-pressure-entropy phase diagram.
The above organic insulating material constituting the first insulating layer includes fluorine-free polymers such as polyaryl ether, benzocyclobutene (BCB) and polyimide; fluorine-containing polymers such as fluorine-added polyimide, tetrafluoroethylene, cycloperfluorocarbon, fluorinated polyaryl ether and fluorine-added parylene; organic SOG, silicon oxide xerogel, and amorphous carbon.
In the forming method of the present invention, the step (C) preferably has the steps of:
(C-1) substituting pure water for the fluid,
(C-2) substituting an alcohol solvent for the pure water, and
(C-3) substituting the raw material solution for the alcohol solvent. Through the above steps, the fluid can be reliably replaced with the raw material solution containing a raw material for forming the second insulating layer.
The above alcohol solvent includes methyl alcohol, ethyl alcohol, n-propyl alcohol and isopropyl alcohol.
In the forming method of the present invention, the raw material solution may be a solution containing an organic polymer formed by hydrolyzing a silicon alkoxide and dehydration-condensing the resultant silicon hydroxide. The step of drying off the raw material solution in the above step (D) may include the steps of (D-1) substituting a supercritical fluid for the solvent in the raw material solution and (D-2) removing the supercritical fluid, or may be the step of removing the solvent in the raw material solution under a pressure equal to, or lower than, atmospheric pressure.
Specifically, the above organic polymer formed by hydrolyzing a silicon alkoxide and dehydration-condensing the resultant silicon hydroxide includes alkoxysilanes [HxSi(OR)4xe2x88x92x in which x=1, 2 or 3 and R is an alkyl group] such as tetraethoxysilane (TEOS), tetramethoxysilane and triethoxysilane. Specifically, the supercritical fluid used for substituting it for the solvent in the raw material solution includes carbon dioxide (CO2) and alcohols such as methyl alcohol and ethyl alcohol.
Otherwise, in the forming method of the present invention, the raw material solution may be a solution containing an organic polymer containing carbon and fluorine or a condensate thereof. The step of drying off the raw material solution in the above step (D) may include the steps of (D-1) substituting a supercritical fluid for the solvent in the raw material solution and (D-2) removing the supercritical fluid, or may be the step of removing the solvent in the raw material solution under a pressure equal to, or lower than, atmospheric pressure.
Specifically, the organic polymer containing carbon and fluorine or the condensate thereof includes cycloperfluorocarbon, fluorine-added polyimide, tetrafluoroethylene, fluorinated polyaryl ether and fluorine-added parylene. Specifically, the supercritical fluid used for substituting it for the solvent in the raw material solution includes carbon dioxide (CO2) and alcohols such as methyl alcohol and ethyl alcohol.
Prior to the step (A), the forming method of the present invention preferably includes the step of forming a protective insulating layer on the substratum for protecting the substratum from the fluid (first-insulating-layer dissolving fluid) which dissolves the first insulating layer. If formed, the protective insulating layer serves to reliably prevent damage on the substratum when the first insulating layer is dissolved. The protective insulating layer includes SiN, SiON, SiC and SiOC.
In the forming method of the present invention, the substratum includes a semiconductor substrate; a lower insulating layer formed on or above a semiconductor substrate; a semiconductor substrate having a semiconductor device or a lower wiring layer; a lower insulating layer formed on or above a semiconductor substrate having a semiconductor device or a lower wiring layer; a combination of a lower wiring layer and a lower insulating layer formed on or above a semiconductor substrate; a combination of a connection hole (which generically refers to a contact hole, a via hole and a through hole) and a lower insulating layer formed on or above a semiconductor substrate; and a combination of a lower wiring layer, a connection hole and a lower insulating layer formed on or above a semiconductor substrate. The wiring includes a wiring line, a connection hole, an electrode, a combination of a wiring line and a connection hole, a combination of a wiring line and an electrode, a combination of a connection hole and an electrode, and a combination of a wiring line, a connection hole and an electrode. The material constituting the wiring includes metals such as copper, aluminum, gold and tungsten, compounds of these metals, and alloys of these metals.
In the forming method of the present invention, since the second insulating layer is formed at least between the wirings without dry etching the second insulating layer in the step (D), it is not required to form a resist mask on the second insulating layer. Unlike a conventional method, therefore, no damage is caused on the second insulating layer by the removal of the resist mask.
In the step (C), further, since the fluid is replaced with the raw material solution without bringing the wiring into contact with a gas, no water droplets are formed between the wirings. Therefore, the wiring is free from a phenomenon that a stress is caused between the wirings due to a surface tension of the water droplets and the wiring is mechanically deformed due to the stress and is broken.
In the step (D), at least a region between the wirings is filled with the second insulating layer in a gelled state in the raw material solution in a state where the wiring is covered with the raw material solution, and then, the raw material solution is dried off, so that the region between the wirings is uniformly. filled with the second insulating layer. Therefore, there is no case where a hollow portion having no second insulating layer formed remains between the wirings, and the region between the wirings is reliably filled with the second insulating layer, so that there is no case where the wiring, a wiring line in particular, vibrates due to a change in Coulomb force between the wirings.
Further, it is no longer necessary to employ the step of removing the second insulating layer by a CMP method, so that the second insulating layer suffers no shear stress caused by polishing, which obviates the destruction of the second insulating layer caused by the shear stress.
According to the present invention, the above object of the present invention is achieved by an apparatus for processing a substratum for removing a first insulating layer filled between wirings formed on a substratum, and then, forming a second insulating layer at least between the wirings,
the apparatus for processing a substratum comprising:
(a) first-insulating-layer removing means for immersing the first insulating layer in a fluid which can dissolves the first insulating layer, to dissolve the first insulating layer into the fluid,
(b) raw-material-solution substituting means for substituting, for the fluid, a raw material solution containing a raw material for forming the second insulating layer, and
(c) drying means for drying off the raw material solution, thereby to form the second insulating layer at least between the wirings.
In the apparatus for processing a substratum of the present invention, the first-insulating-layer removing means and the raw-material-solution substituting means may be structured of one process chamber, that is, may share one process chamber, and the process chamber has:
(d) a substratum supporting stage which is disposed in the process chamber and is for supporting the substratum thereon, and
(e) a substratum transfer portion provided in the process chamber, and
wherein:
the first-insulating-layer removing means further has:
(a-1) a fluid supply source for supplying the fluid for dissolving the first insulating layer,
(a-2) a piping connected to the fluid supply source, and
(a-3) a nozzle which is connected to the piping, is disposed in the process chamber and is for supplying the fluid for dissolving the first insulating layer to the substratum, and
the raw-material-solution substituting means further has:
(b-1) a processing fluid supply source,
(b-2) a piping connected to the processing fluid supply source, and
(b-3) a nozzle which is connected to the piping, is disposed in the process chamber and is for supplying the processing fluid to the substratum.
A structure of a combination of the above-structured first-insulating-layer removing means and the above-structured raw-material-solution substituting means will be referred to as a xe2x80x9cfirst-structured apparatusxe2x80x9d for convenience hereinafter.
Otherwise, the apparatus for processing a substratum of the present invention may have a structure in which:
the first-insulating-layer removing means has:
(a-1) a process chamber,
(a-2) a substratum supporting stage which is disposed in the process chamber and is for supporting the substratum thereon,
(a-3) a substratum transfer portion provided in the process chamber,
(a-4) a fluid supply source for supplying the fluid for dissolving the first insulating layer,
(a-5) a piping connected to the fluid supply source, and
(a-6) a nozzle which is connected to the piping, is disposed in the process chamber and is for supplying the fluid for dissolving the first insulating layer to the substratum, and
the raw-material-solution substituting means has:
(b-1) a process chamber,
(b-2) a substratum supporting stage which is disposed in the process chamber and is for supporting the substratum thereon,
(b-3) a substratum transfer portion provided in the process chamber,
(b-4) a processing fluid supply source,
(b-5) a piping connected to the process fluid supply source, and
(b-6) a nozzle which is connected to the piping, is disposed in the process chamber and is for supplying a processing fluid to the substratum. Each of the above-structured first-insulating-layer removing means and the above-structured raw-material-solution substituting means will be referred to as a xe2x80x9csecond-structured apparatusxe2x80x9d for convenience hereinafter.
Otherwise, the apparatus for processing a substratum of the present invention may have a structure in which:
the first-insulating-layer removing means has:
(a-1) a process chamber which has an opening portion and is for receiving the substratum therein,
(a-2) a lid for hermetically closing the opening portion,
(a-3) a fluid supply source of the fluid for dissolving the first insulating layer,
(a-4) a fluid supply means which is connected to the fluid supply source and is for introducing the fluid into the process chamber,
(c-5) a fluid discharge means for discharging the fluid introduced into the process chamber, and
(c-6) a heating means for heating the fluid introduced into the process chamber, and
the raw-material-solution substituting means has:
(b-1) a process chamber,
(b-2) a substratum supporting stage which is disposed in the process chamber and is for supporting the substratum thereon,
(b-3) a substratum transfer portion provided in the process chamber,
(b-4) a processing fluid supply source,
(b-5) a piping connected to the process fluid supply source, and
(b-6) a nozzle which is connected to the piping, is disposed in the process chamber and is for supplying a processing fluid to the substratum.
The above-structured first-insulating-layer removing means will be referred to as xe2x80x9cthird-structured apparatusxe2x80x9d for convenience hereinafter. The third-structured apparatus is suitable for carrying out the processing with a supercritical fluid. The raw-material-solution substituting means is the above second-structured apparatus.
The fluid supply means (first-insulating-layer dissolving fluid supply means) in the first-insulating-layer removing means preferably has a pressure-temperature control means which is connected to the fluid supply source (first-insulating-layer dissolving fluid supply source) and is for controlling the pressure and temperature of the fluid (first-insulating-layer dissolving fluid) for dissolving the first insulating layer at predetermined levels, and a fluid supply port which is connected to the pressure-temperature control means and is disposed in the process chamber. The fluid discharge means in the first-insulating-layer removing means preferably has a fluid discharge port disposed in the process chamber and a discharged liquid separation apparatus connected to the fluid discharge port through a discharge pressure valve.
In the apparatus for processing a substratum of the present invention, the drying means can have a structure having:
(c-1) a process chamber which has an opening portion and is for receiving the substratum therein,
(c-2) a lid for hermetically closing the opening portion,
(c-3) a fluid supply source of a fluid for drying off the raw material solution,
(c-4) a fluid supply means which is connected to the fluid supply source and is for introducing the fluid into the process chamber,
(c-5) a fluid discharge means for discharging the fluid introduced into the process chamber, and
(c-6) a heating means for heating the fluid introduced into the process chamber.
The above-structured drying means is an apparatus having the above third-structured apparatus.
The fluid supply means (drying fluid supply means) in the drying means preferably has a pressure-temperature control means which is connected to the fluid supply source (drying fluid supply source) and is for controlling the pressure and temperature of the fluid for drying off the raw material solution at predetermined levels, and a fluid supply port which is connected to the pressure-temperature control means and is disposed in the process chamber. The fluid discharge means in the drying means preferably has a fluid discharge port disposed in the process chamber and a discharged liquid separation apparatus connected to the fluid discharge port through a discharge pressure valve.
Otherwise, in the apparatus for processing a substratum, the drying means preferably comprises a drying apparatus.
The following Table 1 shows combinations of the first-structured apparatus, the second-structured apparatus, the third-structured apparatus and the drying apparatus which constitute the apparatus for processing a substratum of the present invention. In Table 1, xe2x80x9c1stxe2x80x9d stands for the first-structured apparatus, xe2x80x9c2ndxe2x80x9d stands for the second-structured apparatus, xe2x80x9c3rdxe2x80x9d stands for the third-structured apparatus, and xe2x80x9cDAxe2x80x9d stands for the drying apparatus.